Surfactant compositions



' proofing, pickling, and other operations.

3,79,416 Patented Feb. 26, 1963 This invention relates to improvements in the art of cleaning objects, particularly those made of metal, glass, etc.

Broadly stated, the invention pertains to alkaline cleaning and, more particularly, to surfactants for use in akaline metal cleaning baths.

An object of the invention is to improve the cleaning efiiciency of alkaline metal cleaners.

Other objects of the invention will in part be obvious and will in part be disclosed hereinafter.

Alkaline cleaners are the most widely used means in industry for cleaning metal, glass, certain plastics, etc. They are primarily used to prepare metals such as steel, brass, and copper for plating, painting, enameling, rust tion includes the removal of various types of soil such as cutting oils, grinding, butting, stamping, and drawing compounds used in various metal-forming operations, as well as rust preventatives, lubricating greases, and various forms of dirt. The alkaline cleaning solutions may be used for soaking, spraying, or electrolytic types of cleaning. 01' these, the soaking or tank cleaning technique is most important because of its widespread use in industry.

In the soaking method of cleaning, the article to be cleaned usually is dipped in or slowly transported through a hot alkaline solution with little or no agitation present. The cleaning solutions employed generally are made of materials consisting of between about 88 to 99 percent by weight of various alkalies, such as caustic soda, sodium metasilicate, soda ash, trisodium phosphate, and tetrasodium pyrophosphate, and from about 1 to 12 percent by weight of a surfactant. Previously, the most widely used surfactants for this purpose have been alkylaryl sulfonates and rosin soaps. Usually, the concentration of the cleaning materials (alkali plus surfactant) in the tank or bath is maintained between 2 and percent of the cleaning solution.

As oil, grease, and other soils are caused to be separated from the part being cleaned in the tank, a scumlike layer collects at the top of the bath. If the surfactant employed is not thoroughly soluble in the hot alkaline solution, it also will tend to accumulate in this surface layer. When the accumulation of scum in the surface layer becomes so great that it tends to coat the otherwise clean part as it is withdrawn from the bath, it becomes necessary to skim the soil and undissolved surfactant from the top of the tank. Each time this is done, a considerable amount of the surfactant is removed and, of course, this tends to lower the concentration of the effective cleaning agents in the bath to a point where the operation of the bath becomes unsatisfactory much sooner than it otherwise would if such losses could be minimized or eliminated. One obvious solution to this problem is to employ only surfactants that are soluble in hot alkaline solutions.

There are available poiyoxyalkylated tert.-carbinamines which are known to have a detergent effect on metal surfaces and would appear to have other requisite characteristics for alkaline cleaning purposes. These compositions, which have been disclosed in copending U.S. application Serial No. 632,648, now U.S. Patent No. 2,871,266 have Such preparaa structure which may be generally represented by the following formula:

in which R R and R are alkyl groups whose total carbon atom content ranges from 7 to 23, and m is an integer of 6 to 101.

The difliculty with compounds of the above-mentioned formulas is that they lack the requisite solubility property in hot alkaline solutions, such as, for example, 5 percent sodium hydroxide. It was thought that this lack of desired solubility could be overcome by completely (or essentially so) sulfating the compounds so as to obtain products having the following formula:

in which the values for R R R and m are the same as indicated above, and X is a monovalent cation such as an alkali metal or hydrogen. However, when a number of these compounds were sul'fated, they were found to have a materially decreased cleaning efiiciency notwithstanding the fact that the product was quite soluble in hot alkaline solutions. This effect appeared difficult to explain or otherwise account for, and so efforts were made to determine the mechanism of this change in cleaning performance.

In the course of the investigation which ensued, it was discovered that not all of the polyoxyalkylated tert.-carbinamines would function efiiciently as metal cleaners after they had been sulfated. Specifically, the sulfated amines which proved to be useful were those having the following formula:

in which R -|-R +R =l1 to 14, m is an integer of from 6 to 101, and X is a monova-lent cation such as an alkali metal or hydrogen.

A further discovery was that of these sultfated amines which had been demonstrated to possess utility as metal cleaners, only those having a certain narrow range of ethylene oxide units namely between 12.5 and 17.5, gave metal cleaning results which are substantially as good as the results obtained with the non-sulfated compositions. At the same time, these compounds containing the indicated narrow range of ethylene oxide units also had the added advantage of complete solubility in the hot alkaline solution and thereby eliminated the objection described above, namely, the excessive losses caused when the surface of the cleaning baths had to be skimmed to remove the skum-like layer.

In actual practice, the preferred composition is an alkali metal salt, generally the sodium salt, of the tertcarbiuamine-ethylen'eoxide 12,5415 sulfate. Such compounds are completely soluble in 5 percent sodium hydroxide at temperatures of 01( 0 C. They are also soluble in concentrations such as 10 percent caustic, although not throughout this entire temperature range.

The following examples describe in detail the alkaline metal cleaning test method which was employed to establish the principal utility of the present invention. Following Example 1, Table I lists a series of sulfated tert.-carbinamine-ethylene oxide compounds and indicates the cleaning efliciency of each of those compounds as tested by the method described below. In this series,

in metal cleaning baths, whereas products above and be-.

low that range perform unsatisfactorily.

Example 1 The following test method was used for evaluating the, comparative efficiences of various alkaline metal cleaners. The method was adapted from a procedure used throughout the industry and which is described by- S. Spring, H. Forman, and L. Peale in Method of Evaluating Metal Cleaners, Ind. & Eng. Chem., Analytical Edition, vol. 18, No. 3, pp. 201-204 (1946). Briefly, the test consists of carefully cleaning thin SAE 1010 steel panels (3" x 3") and uniformly coating them with a thin film of brightstock mineral oil (Saybolt viscosity 150 sec. at 210 F.) which is drained for one hour at 35 C. The coated panel is then rotated for 5 minutes at 30 rpm. in a 1000 ml. beaker of the solution being tested. That solution, which is maintained at a temperature of 82 :2" C. irran oil bath, consists of 5 percent of the detergent being tested. The detergent consists of 3 percent active surfactant, 31 percent sodium hydroxide, 31 percent sodium carbonate, and 35 percent sodium metasilicate pentahydrate. (The actual concentration of the surfactant inthe cleaning bath was 0.15 percent.)

Following this period of alkaline cleansing, the panel is'rinsedin an overflowing beaker of warm water which is approximately 40 C., allowed to drain in air for 20 seconds, and then subjected to a light spray of deionized Any. area on the panel which is still coated with residual oil.

Water for approximately seconds on each side.

will exhibit readily visible droplets which are termed water breaks. On clean areas, a continuous water film will be observed. By means of a transparent plastic sheet which is the size of the test panel, and which has been ruled oil into 100 squares of uniform dimensions, it is possible to determine the percentage of surface area which does not show any water breaks. This value represents an index of the cleaning eliiciency of the alkaline cleaner which has been used. Three such panels are run, readings taken for each side of each panel, and the average of the six sides is considered to represent the cleaningefiiciency index for the particular cleaner composi-. tion being tested. For the particular oil and the concentration of surfactant used, etc., the limit of acceptability has arbitrarily been set at 80 percent or above, these being values that have been found to represent levels of cleaning efiiciency which are acceptable in a representative number of typical industrial applications.

Employing tests such as described above for each of the cleaning compositions, which differed from one another only bythe nature of amine surfactant which was included, results obtained were as indicated in Table I *No'ML-The surfactants employed were snlfated, polyethoxylatcd t-alkyl amines, the amines being a commercially available mixture in the ranges tC12-15H25-31NH2, The surfactants were all in the sodium form. The formula for the sulfated amines may be represented as t-C12-1sH25-:nNH (CsHiO) 111 S OaNa 7 lnwhich mzthe number of units per unit of amine shown in the first column above.

Example 2.

Following the procedure of Example 1, a comparable cleaning composition is obtainable by employing t-C H NH instead of. the mixture of amines. This amine also is sulfated and the ethylene oxide content of the polyethoxylated product is between 12.5 and 17.5 units per unit of amine.

Example Following the procedure of Example 1, a comparable cleaning composition is obtainable by employing t-C H NH instead of the mixture of amines. This amine also is sulfated and the ethylene oxide content of" the polyethoxylated product is between 12.5 and 17.5.

units per unit of amine.

Example 4 set forth in Example 1 is obtained; i.e., the same relative performance is obtained with respect to the various contents of ethylene oxide in the difierent surfactants.

Example 5 The procedure of Example 1 is repeated except that, instead of employing panels of SAE 1010 steel, copper panels are employed. A cleaning result very close to that set forth in Example 1 is obtained.-

Exampleo The procedure of Example 1 is repeated except'that,

instead of employing panels of SAE 1010 steel, stainless steel panels are employed. A cleaning result very close to that set forth in Example 1 is obtained.

It is readily apparent from the foregoing examples, and particularly the data in Table i, that the amine surfactants having from 12.5 to 17.5 units of ethylene oxide are above the level of acceptability (minimum of percent) indicated previously with regard to their comparative cleaning efficiencies. The compounds having less or more than those amounts are, by the same token, not acceptable. Aiurther indication of the comparative effectiveness. of

the present invention may be had ,fromthe fact that a commercially available alkyl aryl sulfonate, whichheretofore had been considered to be among the finest surfactants known for alkaline metal cleaning applications, only rated a 31 percent cleaning efiiciency index under identical test conditions.

The various amines described above can be prepared by procedures similar to that disclosed in copending US.

application Serial No. 632,648 and may be sulfated by any of several well-known methods, using sulfuric acid, sulfur trioxide, chlorosulfonic acid or other suitable sulfating agents. In Examples 7 and 8 are described preparations for two amines by a suitable process (the latter being the polyoxyethylene adduct of the amine produced in the former example). In Examples 9 and 10 are described typical preparations of a sulfated amine in ccordance with the present invention.

Example 7 In a suitable reaction vessel there were combined 500' g. (2.54 mols.) t-dodecylamine, 45.8 g. (2.54 mols.) water, and g. methanol. 80 C. and 139 g. (3.05 mols.) of ethylene oxide were added at 8085 C. over a period of 2 to 8 hours, At the end of this time, the product was isolated by distillation to remove the methanol and water. The yield of product (N(t-dodecyl)ethanol amine) amounted to 618.2 g. and had a neutral equivalent of 246.8. This was equivalent to N-("-dodecyl)amine combined with 1.18 mols. of ethylene oxide. This neutral equivalent indicated that the product contained a small amount of the diethanol amine.

This mixture was heatedto.

Example 8 In an appropriate reaction vessel, there were combined 402.3 g. N-(t-dodecyDethanol amine (from above), having a neutral equivalent of 246.8, with 989.7 g. ethyleneoxide in the presence of 1.6 g. powdered potassium hydroxide at 140-180 C. When the reaction was cornplete, the catalyst was neutralized by the addition of a strong acid. The isolated product amounted to 1392.2 g. of a. light yellow liquid which tended to solidify on standing at room temperature. This product (t-dodecylamine-ethyleneoxide had a neutral equivalent of 855.5 which was equivalent to t-dodecylamine combined with 15 mols. of ethylene oxide.

Example 9 To a 1-liter, three-necked flask containing 17.6 g. (0.2 mol.) dioxane and 150 cc. carbontetrachloride, cooled to -10, was added dropwise, with good agitation, a cooled solution C.) of 17.6 g. (0.22 mol.) liquid S0 dissolved in 150 cc. carbontetrachloride. When this addition was complete a second solution, containing 171.1 g. t-dodecylamine-ethyleneoxide (0.2 mol.) dissolved in 300 cc. carbontetrachloride, was added dropwise over a 1-hour period at 0-20 C. This solution was stirred for an additional 30 minutes at 0-20 C. after completion of the addition. This reaction mixture was then neutralized by the careful addition of 9.6 g. (0.24 mols.) sodium hydroxide dissolved in 400 cc. water. The resulting thick emulsion was allowed to stand in a separatory funnel until separation of the carbontetrachloride was complete. Stripping of the aqueous layer gave 180.2 g. of a light amber viscous oil. (Viscosity=33,400 cps.)

Analysis of the product (t-alkylamino-polyoxyethylene sulfate) gave the following results:

Analysis-Calculated: N, 1.47; S, 3.36; sulfated ash 7.52. Found: N, 1.48; S, 3.27; sulfated ash 5.81.

This product was found to be soluble in boiling 5 percent and 7 percent NaOH.

Example 10 In a suitable reaction vessel, there were combined 213.5 g. (0.25 mol.) t-alkylarninopolyoxyethylene with 100.0 g. (1.0 mol.) 98 percent sulfuric acid, at a temperature of 6065 C. over a 2-hour period. At the end of this time, there was mixed with this reaction mixture 81 g. (2.03 mols.) NaOH dissolved in 800 cc. of water. After separation of the excess sodium sulfate,

the product (239 g. of t-alkylamino-polyoxyethylene sulfate) was isolated as a pale amber, viscous liquid (viscosity, 33,000 cps.).

It will be apparent to anyone skilled in the alkaline cleaner art that certain variations from the compositions and methods set forth above by way of illustration are readily feasible without departing from the scope of the present invention. For example, although the specific examples described a typical alkaline cleaning composition made with sodium hydroxide, other alkalies of high pH may be employed. Nor must the percentages of the alkali and surfactant be limited to the 5 percent and 0.15 percent, respectively, that were employed by way of illustration in the examples. Nor must the surfactants be made by the particular methods herein described. The surfactants which are the subject of the present invention are readily soluble in lower or higher concentrations of alkali and will, within the stipulated ranges of ethylene oxide content, perform with comparable efiiciency in the cleaning of metal and other surfaces. Moreover, the amounts of surfactant may be varied with a proportionate effect on cleaning efiiciency. Still other modifications are possible, all obviously within the scope of the following claims.

We claim:

1. A surfactant composition essentially consisting of a compound having the formula in which R R and R are alkyl groups having a total of 11 to 14 carbon atoms, In has a value of from 12.5 to 17.5, and X is a monovalent cation selected from the class consisting of hydrogen and the alkali metals.

2. The composition of claim 1 in which X is sodium. 3. The composition of claim 1 in which X is hydrogen. 4. The composition of claim 1 in which X is potassium.

References Cited in the tile of this patent UNITED STATES PATENTS 1,970,578 Schoeller et al. Aug. 21, 1934 2,746,932 Vitale May 22, 1956 2,755,296 Kirkpatrick July 17, 1956 2,768,956 Scott Oct. 30, 1956 

1. A SURFACTANT COMPOSITION ESSENTIALLY CONSISTING OF A COMPOUND HAVING THE FORMULA 